With the rapid development of electronics one can find electric power converters, such as DC-DC and AC-DC converters, almost everywhere. In the search for an increasing power density, the switching frequency is being raised and multilevel converters are being used, reducing the size of passive filtering components.
The filtering components use a great portion of the volume of a power converter. To further reduce the size much effort is made in the development of (new) multilevel and multicell converter topologies, and modular converter structures. By using a higher number of levels, opposed to only two, the ripple, and consequently the volume of filtering components is reduced. Several popular examples of such multilevel/multicell converters include the flying capacitor converter, neutral-point clamped converter, cascaded cell multilevel converter and modular multilevel converter. However, current multilevel topologies have poor (linear) scaling of the levels with respect to the number of switches. There are multilevel topologies that scale exponentially with the number of switches, but these topologies require isolated voltage sources or they can not supply active power from each level.
Another point of concern is the reliability of power electronics. In most cost-driven applications, a single component failure immediately results in a defective product. To ensure sufficient reliability, power semiconductors are not used up to their full potential. A basic circuit that is applied in most power converter topologies is the commutation cell, which includes two switches, one inductor and one capacitor. The switches can be stressed more when making the circuit single-fault safe. However, this comes at a high cost: i.e. adding another six switches and drivers, and replacing each switch with two parallel branches of two series switches. This high cost for single-fault safe operation, also applies to the known multilevel converters such as the flying capacitor and neutral-point clamped converter, making it generally not interesting to implement except for special applications, such as aerospace ones.
Accordingly, it would be an advance in the art to provide multilevel power converters having improved scaling of output levels with respect to the number of switches and also having improved fault tolerance.